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How to Calculate LOD & LOQ

In analytical chemistry, the terms LOD and LOQ stand for limit of detection and limit of quantification, respectively. The LOD is the smallest sample of a substance that can be used to detect blank or negative samples; the LOQ is the smallest amount of a substance for which data can be collected with a high degree of confidence. Calculating LOD and LOQ requires the slope of your data set and the standard deviation.

Things You'll Need

Standard deviation of measurement within your sample
Slope of data set

Instructions

Calculate LOD
- 1
  Multiply 3 times the standard deviation of the data set.
- 2
  Divide the product by the slope of the calibrated curve from your data.
- 3
  Put the equation together to obtain the LOD. For example, if your standard deviation is 15853 and your slope is 4250, your equation will be:
  
  (15853*3)/4250 = 11.19.
  
  Your LOD for this sample is 11.19.
Calculate LOQ
- 4
  Multiply the standard deviation of your data set by 10.
- 5
  Divide the product by the slope of your sample.
- 6
  Put the equation together to obtain LOQ. For example, for a standard deviation of 12895 and a slope of 5500, your equation will be:
  
  (12895 * 10)/5500 = 22.45.
  
  22.45 is the LOQ.

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